AC start, solar run hybrid solution for single phase, starting capacitor, motor applications with solar power measurement

ABSTRACT

An induction-type AC electric motor system has a variable frequency motor (VFD) drive having at least two outputs, the VFD drive coupled to be powered by a solar input and to power the motor with a switching device in a first setting. With the switching device in a second setting, a run winding of the AC electric motor couples to an AC input and a start winding of the AC motor couples through a capacitor and start switch to the AC input. The system is configured to, upon determining motor start, put the contactor in first setting and use the VFD drive to continue running the motor, and, when the AC motor is not rotating, the system is configured to periodically measure available solar power and to start the AC motor if the available solar power exceeds a first threshold power determined sufficient to run the AC motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present applicant is a continuation-in-part of U.S. patentapplication Ser. No. 16/786,533 Filed: Feb. 10, 2020 which is acontinuation-in-part of PCT/US19/19881 filed Feb. 27, 2019 and claimspriority to U.S. patent application Ser. No. 15/907,035 filed Feb. 27,2018 (now U.S. Pat. No. 10,560,033).

BACKGROUND

AC Electric motors are widespread and used in many applications. Thereare two general groups of AC motors based on the electrical supply:single-phase and three-phase. Single phase motors are typically used inhousehold and small power applications, while three phase motors aremainly used in industrial applications where a three-phase electricitysupply is provided.

75% of all AC motors are singe phase motors, compared to 25% of threephase ones, but the power level of single phase motors is typicallysignificantly less than those supplied by three phase electricity. Manysingle-phase AC motors are induction motors with a starting windingcoupled through a starting capacitor and starting relay or switch toassist in producing a rotating magnetic field, thus giving a startingtorque so that they may begin rotating when power is applied.

Single-phase AC induction motors with starting capacitors draw enormouspower surges when full-voltage, full-frequency, AC power is applied tothem; these power surges end soon after the power is applied to themotor as power drawn by the motor drops back to a much lower “run” powerrequirement. Motor starting power surges may reach eight or more timesrun power requirements. These motor starting power surges may, and oftendo, exceed power available from solar photovoltaic panel arrays even ifthose solar panel arrays are large enough, and solar irradiancesufficient, to sustain run power requirements at the time motoroperation is desired.

Most common household motor loads are 3-wire, single phase, inductionmotors with startup capacitors. Running this kind of motor loads throughsolar power is an economical, but not always efficient. The problem isthe part of the day with low solar irradiance, especially early in themorning and late afternoon. Single phase motors require high inrushstartup currents, which is difficult to provide during low irradiancetime of the day.

While insolation measurement of solar panels is possible, poweravailability from solar panels may vary because of partial shading andother effects. Direct measurement of power availability is difficultwithout coupling a load to the panels or attempting to start a motor.

SUMMARY

We propose using a non-solar AC source such as the electrical grid forstarting single phase motor loads, but then once the motor started,quickly switching the motor to be driven from a solar energy source.This apparatus could be used for demand-response as well as peak powershaving purposes, to decrease power consumption from the AC grid, whilestill having critical single-phase loads operate.

A proposed solar hybrid solution for single phase motors with startingcapacitor solves the problem of not having enough solar power forstarting a single-phase AC motor but having enough solar power to runthe single-phase motors from solar power, with modes for measuring thesolar PV power availability to know when there is enough solar power, sothat AC grid power can be used to start the system, and solar will takeover.

In an embodiment, an induction-type AC electric motor system has avariable frequency motor (VFD) drive having at least two outputs, theVFD drive coupled to be powered by a DC solar input and to power themotor with a switching device in a first setting. With the switchingdevice in a second setting, a run winding of the AC electric motorcouples to an AC input and a start winding of the AC motor couplesthrough a capacitor and start switch to the AC input. The system isconfigured to, upon determining motor start, put the contactor in firstsetting and use the VFD drive to continue running the motor, and, whenthe AC motor is not rotating, the system is configured to periodicallymeasure available solar power and to start the AC motor if the availablesolar power exceeds a first threshold power determined sufficient to runthe AC motor.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a wiring diagram of a single-phase induction motor withstarting capacitor and starting relay in a starting winding circuit, arunning or main winding in a main circuit, with overload protectioncommon to both circuits.

FIG. 2 illustrates schematically a single-phase motor powered by a DC(solar or battery) source and driven by a Variable Frequency Drive (VFD)using the starting winding with a separate phase of the VFD.

FIG. 3 illustrates a linear voltage versus frequency operating curve foruse in controlling the VFD.

FIG. 4 illustrates a typical voltage current curve of photovoltaic paneloutput.

FIG. 5 is a flow chart of a maximum power point tracking algorithm.

FIG. 6 illustrates a motor with a dual-mode motor-control systemsupporting variable frequency motor drive when operating on a solarpower source and a capacitor start motor drive when operating on an ACline power source.

FIG. 7 illustrates a dual-mode control system operating a motor, themotor having a two-independent-phases VFD driven by solar power duringdaylight and a single phase with neutral AC input and starting capacitorat night.

FIG. 8 illustrates an embodiment having a system with two controllers incommunication with each other and an electric-rate receiver to optimizecost of pumping in a water system.

FIG. 9 illustrates components included in a motor controller assemblyassociated with the system of FIG. 7 .

FIG. 10 is a schematic diagram illustrating an alternative embodimenthaving a motor with a dual-mode motor-control system supporting startinga capacitor start motor on AC line power and configured to switch tousing a variable frequency motor drive when solar power is available andit is possible to run the motor on a solar power source.

FIG. 11 is a flowchart illustrating operation of the embodiment of FIG.10 .

FIG. 12 is a waveform illustrating voltage across the run winding aftera motor is started on AC line power as power to the motor switches tothe variable frequency motor drive.

FIG. 13 illustrates a motor with a dual-mode motor-control systemresembling that of FIG. 10 supporting a capacitor start motor, thatstarts the motor on an AC line power source and switches to run on avariable frequency motor drive powered by a solar power source, withadded switches on the solar input side for measuring available current(IOC) from the solar PV panels.

FIG. 14 illustrates a motor with a dual-mode motor-control systemresembling that of FIG. 10 supporting a capacitor start motor drive,that starts the motor on an AC line power source and switches to run themotor on a variable frequency motor drive powered by a solar powersource, with added switches and an associated resistor bank in the DClink circuit for measuring available power from the solar PV panels.

FIG. 15 illustrates an embodiment incorporating a three-phase variablefrequency motor drive where the first and second phases are coupled tothe motor and the third phase is coupled to a resistor that is drivenonly while measuring available solar power.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates schematically a single-phase induction motor 100including starting capacitor 102 and starting relay 104 in a startingwinding 106 circuit. A running or main winding 108 is in a main circuit,with overload protection as a common block.

Single phase induction motors 100 require a second phase applied tostarting winding 106 to induce initial rotation, or start, in additionto power applied to the main winding 108, the starting winding providinga magnetic field phase shifted, in most embodiments about 90 electricaldegrees, in respect to the main winding. The starting winding 106 allowsthe motor to create a starting torque. The phase shift applied to thestarting winding is typically achieved with capacitor 102 in series withstarting winding 106. Once the motor starts rotating, there is no needfor starting winding 106; the starting winding is typically disconnectedafter rotation begins because it dissipates heat when in the circuit.Switch or starting relay 104 disconnects the starting winding 106 fromthe circuit once the motor starts. The starting relay 104 can sensecurrent or voltage limits, but the most common type in surface motors isa centrifugal relay that opens when the motor shaft speed reaches around80% of rated speed. The starting winding 106 with starting capacitor 102thus drops out of the circuit leaving only the main winding 108energized, after the motor 100 starts rotating.

The same single-phase motor 148 (FIG. 2 ) can be run by a three-phasevariable frequency drive 150 powered from a solar source 170, if thewire that connects starting winding 153 to start relay 152 isdisconnected from start relay 152, and connected directly to a startingphase PH2 154 of the three-phase variable frequency drive 150. That way,starting capacitor and the relay are not in the starting winding circuitanymore. Once the motor has started rotating, the starting phase 154 ofthe variable frequency drive may drop out of the circuit, leaving themain phase PH3 156 and common return PH1 158 coupled to the main or runwinding 160.

Variable frequency drives (VFDs) typically have six power switches (Q1to Q6), configured as a three-phase inverter. Each switches Q1-Q6 iscontrolled by microcontroller 162 that generates pulse-width modulated(PWM) signals at a high switching frequency, typically on the order offew to a hundred kilohertz, to generate an approximately sinusoidalcurrent signal on each phase of the motor winding. Such VFDs can be feddirectly by a solar power source, but also a voltage boost circuit 164may be used when input DC voltage Vdc is insufficient for proper VFDoperation. Boost circuit 164 has at least one high switching frequencypower switch, controlled by a boost control signal generated atmicrocontroller 162. The boost circuit 164 regulates a DC link 166, 168voltage that feeds switches Q1-Q6 of the VFD. Microcontroller 162 readsDC link and input solar 170 voltages to generate appropriate dutycycle-boost control signals for controlling boost circuit 164, in turnregulating voltage on DC link 166, 168.

Before connecting to variable frequency drive (VFD), a single-phasemotor with start capacitor can be rewired as a three-wire single phasemotor, if the wire that connected starting winding to start relay isdisconnected from the start relay. Furthermore, if existing running(main) winding is connected to phases: Ph1 and Ph3, and a “starting”winding is connected to Ph2 154, the start capacitor and relay areremoved from the starting winding circuit. the running winding voltage(Vr) can be shown as: Vr=Vph3−Vph1,

while voltage across starting winding (Vs) is: Vs=Vph2−Vph1.

PWM signals for all six power switches (Q1-Q6) are generated bymicrocontroller 162 to create voltages Vph1, Vph2 and Vph3. Phases Vrand Vs are generated approximately 90 electrical degrees apart, tocreate starting torque that starts the motor. Microcontroller 162 cansense the moment motor starts rotating, by monitoring input DC voltagefrom solar DC source 170.

During start-up, microcontroller 162 generates PWM signals to create PH2154 and PH1 158 voltages during each attempt to start the motor, as wellas return voltage 156. The microcontroller increases the effectivevoltage and frequency of both motor winding voltages: Vr and Vsaccording to a V/f motor control algorithm until the generated frequencyreaches 30 Hz, half of full speed for typical 60-Hz motors. Once thegenerated frequency reaches 30 Hz the microcontroller 162 stopsgenerating voltage across the starting winding Vs by not activatingpower switches Q3 and Q4, and checks the input DC voltage Vdc todetermine if motor 148 has started rotating. If the motor has started,the microcontroller continues with a Maximum Power Point algorithm,keeping the voltage/frequency control across the running winding only(Vr). If the microcontroller decided that motor has not started, then itshuts down the PWM signals and tries to start the motor again after atime delay.

Once the motor has started rotating, the VFD continues to generatevoltage Vr across the main winding using power switches Q1, Q2, Q5 andQ6, while leaving switches Q3, and Q4 quiescent as the starting windingis no longer used. Microcontroller controls VFD power switches accordingto frequency/voltage mode illustrated in FIG. 3 . By adjusting motor148's phase voltage and frequency at the same time, the VFD 150 providesvariable speed operation of motor 148. Variable speed operationtypically uses more power at high speeds than at low speeds, allowingadaption of motor power consumption to power available from the solarpower source 170 or to motor's 148 speed requirements.

When VFD 150 is powered by a solar PV source 170, it may use aninstantaneous power no greater than that provided by a power limit thatvaries based on the sun's irradiance (intensity). Therefore, VFD 150uses variable speed control to balance the input solar power with motorload power. The system obtains as much power as possible from solarsource 148 while running the AC motor as a load. Input voltage sensor(Vdc) is used as an input for microcontroller 162, which uses a maximumpower point tracking (MPPT) mechanism to obtain maximum power from solarpower source 170.

MPPT Method:

A typical solar source load curve is illustrated in FIG. 4 . The solarsource has limited power; power available depends on the panels providedin the solar source, solar irradiance and ambient temperature. FIG. 4shows solar load characteristic for a given temperature and irradiance.

Point 1 on FIG. 4 shows the operating point of the solar source at whichit provides maximum power, known as the maximum power point (MPP). Ifsolar source is unloaded, voltage on the terminals of solar source ismaximum, and solar current is zero (point 2), while if solar source isoverloaded the current is maximum and solar source voltage drops towardszero (point 3).

An actual solar source operating point can be anywhere between points 2and 3, but the source provides maximum power if operated at MPP point 1.For some loads, it can be desirable to find the MPP point and operatethe solar source at that point.

Microcontroller 162 has machine readable instructions in memory, knownherein as MPPT firmware, for finding and tracking an MPP point tooperate the solar source at the MPP point according to method 400.

With reference to FIG. 2 and FIG. 5 , method 400 begins withmicrocontroller 162 (FIG. 2 ) measuring 402 voltage (Vdc) and current(Idc) from solar source, it saves a Vdc value for no load condition(Idc=0), an open circuit voltage (Voc) of the solar source170—determining point 2 of FIG. 4 . Microcontroller 162 then initializes404 a reference voltage value Vref, as Vref=Voc*⅚, as an expected MPPvoltage, and it attempts 406 to start the single-phase motor 148 usingPWM signals to drive transistor switches Q1, Q2, Q3, Q4, Q5, and Q6.Once the single-phase motor 148 starts rotating, microcontroller 162increases VFD frequency (and thus motor speed) 408, increasing load onthe solar source 170, to move the solar source's operating point frompoint 2 toward point 1 (FIG. 4 ).

If panel voltage Vdc drops below Vref before motor 148 reaches 30 Hz, orhalf-speed, indicating the solar source is producing insufficient powerto support low speed operation, microcontroller 162 shuts down thevariable speed drive and waits 412 for a timeout period beforeattempting 406 to start the motor 148 again. If Vdc remains above Vrefwith the variable speed drive at 30 Hz and the motor rotating,microcontroller 162 shuts down PH2 154 while continuing to operate PH1158 and PH3 156 to continue operating motor 148.

Once the motor is rotating at half of rated speed with the VFD output at30 hertz or better, operation of the motor and VFD is according to MPPTmethod 990.

The MPPT firmware in microcontroller 162 then measures input solarsource voltage Vdc and calculates 416 two variables:

-   -   Error between reference voltage (initially defined as        (Vref=Voc*⅚)) and instantaneous solar input voltage measured at        input terminals at all times—Vdc→Error=Vref−Vdc. The error value        is positive if instantaneous solar input voltage is lower than        reference voltage Vref, meaning that solar source is loaded        (higher current) more than the expected MPP point, while the        error value is negative if solar source is underloaded with        lower current than at the expected MPP point.    -   Derivative error is a difference in error values defined above        for two successive sampling times of the        microcontroller→dError=Error(z)−Error(z−1), where Error(z) is        error calculated at instantaneous time, while Error(z−1) is        error calculated in previous sampling time of the        microcontroller. Hence, derivative error (dError) is positive if        instantaneous error is higher than error in a previous sampling        time, and negative if it's lower than the previous sampling time        error.

The microcontroller 162 calculates error and derivate error valuesrepeatedly, to provide near-instantaneous values, comparing them withvalues from prior sampling times. Depending on instantaneous andprevious sampling values of error and derivative error themicrocontroller decides whether to increase or decrease operatingfrequency for VFD 150.

-   -   1. If 418 the instantaneous error is positive and derivate error        is positive or equal to zero, then microcontroller 162 decreases        420 the reference frequency signal for VFD 150, meaning that        instantaneous operating point of the solar powered VFD 150        running single phase motor 148 is loading the solar source        beyond MPP point, and should “slow down” in order to get to the        MPP point from FIG. 4 . If 426 VFD 150 and motor 148 frequency        dips below a minimum frequency, such as 30 Hz, microcontroller        162 shuts down VFD 150 and waits 412 for the timeout interval        before attempting 406 to start the motor again.    -   2. If 422 the instantaneous error is negative and derivate error        is negative or equal to zero, then microcontroller 162 increases        424 the reference frequency for VFD 150 up to a maximum        frequency such as 60 Hz, meaning that instantaneous operating        point of the solar powered VFD 150 and motor 148 is below the        MPP point, and the motor should “speed up” while drawing more        power to get to the MPP point 1 (FIG. 4 ).

Apart from using error and derivative error for MPPT, the MPPT methodalso monitors instantaneous absolute value of DC link voltage 166, 168.Boost circuit 164 decouples DC link voltage 166, 168 so the VFD is fedwith constant voltage, so that microcontroller can perform MPPToperation and extract maximum power from solar source. However, if boost164 loses voltage regulation of DC link voltage, DC link voltage will bebelow referenced value, and microcontroller 162 decreases motor'sfrequency by an increment; in a particular embodiment the increment is 5Hz. This unloads the solar source should bring DC link voltageregulation back. However, if stepping back by 5 Hz was not enough, thenthere will be one or more successive 5 Hz step back steps, until VFD 150and motor 148's frequency drops below a minimum operating frequency,such as 30 Hz, after which the microcontroller stops VFD operation—FIG.5 . In a particular embodiment the minimum operating frequency is 30 Hz

This way, it's possible to run single phase motor using a variablefrequency drive powered from solar PV source.

The motor system 500 of FIG. 6 shows a single-phase motor 502 modifiedto have 4 leads where: L1 504 and L2 506 are running (main) winding 512,SW 508 and L2 506 drive the starting winding 514 and SR 510 is astarting capacitor 516 and relay 518 lead. Those four leads areconnected to the single-phase AC source 524 and three leads fromvariable frequency drive through separate contactors 520, 522, as shownin the FIG. 6 . In an alternative embodiment, a three-pole,double-throw, break-before-make relay replaces both contactors 520, 522.

Main winding leads 504 and 506 are connected to AC line and neutralconnections of the AC input 524 respectively through contactor 522, orto PH1 530 and PH3 532 connections of the VFD 526. Starting winding leadSW 508 is connected to starting relay SR lead 504 through contactor 522,or to Ph2 534 of VFD 526 through contactor 520.

Contactors 520, 522 can be energized (actuated) by signals 1 and 2respectively, but are never energized at the same time. Both contactorcontrol signals can be derived from the microcontroller or some otherdevice with simple signal logic outputs, or manually using a switch.

If the DC source is Solar photovoltaic panels (PV), then themicrocontroller or any other logical device may have a solar irradiance(sun intensity) sensor, adapted to sense when solar intensity is belowcertain redefined threshold, then it can switch contactor 520 OFF (usingsignal 2) to disconnect solar PV source, and then turn contactor 522 ON(using signal 1), to connect an AC source. A switching sequence is inreverse when the solar intensity sensor recognizes that solar power isavailable and switches from the AC source 524 back to solar PV sourceand variable frequency drive VFD 526.

In an alternative embodiment, when operation of the motor is desired,the microcontroller determines whether PV panel voltage Vdc is present,if Vdc is present the microcontroller attempts to start the motor onsolar power with contactor 522, 620 off and contactor 520, 624 on. Ifthe motor fails to start, such as when the sun is obscured by cloud,then then the microcontroller switches contactor 520, 624 OFF (usingsignal 2) to disconnect solar PV source, and then turn contactor 522,620 ON (using signal 1), to connect an AC source.

During AC line operation, the system of FIG. 6 is effectively configuredas a normal capacitor-start induction motor. During solar operation thesystem of FIG. 6 is effectively configured as an MPPT—VFD 3-phase drivesystem, with the run winding coupled to PH1 and PH3 and a phase-shiftedstarting winding coupled to PH2, until rotation begins, when PH2 dropsoff.

Hybrid system operation can also be achieved if a time relay is used todrive signals 1 and 2 based on the time of the day, so that in themorning the solar source provides power for VFD 526 and motor 502 in3-wire configuration, while in the evening signal 2 switches thecontactors to activate AC source power to directly drive the motor 502with the starting capacitor 516 in circuit.

An alternative system 600 (FIG. 7 ) has a dual-mode control systemoperating a single-phase induction motor 602, the motor run by atwo-independent-phases VFD 604 driven by solar power during daylight anda single phase with neutral AC input 606 and starting capacitor 608 atnight.

Single phase motor 602 is modified to have 4 leads where: main 610 and aneutral 611 are connected to running (main) winding 612, SW 614 andneutral 611 drive the starting winding 616 and SR 618 is a startingcapacitor 608 and relay 621 connection. Those 4 leads are connected tothe single-phase AC source 606 and two leads plus neutral from variablefrequency drive 604 through separate contactors 622, 624. In analternative embodiment, a two-pole, double-throw, break-before-makerelay (not shown) replaces both contactors 622, 624.

Main winding leads 610 are connected to AC line and neutral connectionsof the AC input 606 respectively through contactor 620, or to PH1 630 ofthe VFD 526. Starting winding lead SW 614 is connected to starting relaySR lead 618 through contactor 620, or to Ph2 632 of VFD 604 throughcontactor 624.

Contactors 622, 624 can be energized (actuated) by signals 1 and 2respectively, but are never energized at the same time. Both contactorcontrol signals can be derived from the microcontroller or some otherdevice with simple signal logic outputs, or manually using a switch.

During AC line operation, the system of FIG. 7 is effectively configuredas a normal capacitor-start induction motor driving by line and neutrallines of the AC input 606. During solar operation the system of FIG. 7is effectively configured as an MPPT—VFD 2-phase drive system, with therun 612 winding coupled to PH1 and a phase-shifted starting winding 616coupled to PH2 until rotation begins, after which PH2 drops off leavingthe starting winding 616 undriven.

In an alternative embodiment 800 (FIG. 8 ), a power price receiverdevice 802 is coupled to microcontroller 162 of at least one of twocontrollers 804, 806 according to FIG. 6 or FIG. 7 to receive rate dataindicating periods of high cost electricity. In this embodiment, solarpanels 808 provide solar power part, but not all, of each day; a firstcontroller 804 is configured to run a deep well pump motor 810 on solarpower if available, and on AC line 812 if sufficient power is available,however controller 804 is configured to run deep well pump motor 810only if a water level in a cistern 814 is below a threshold asdetermined by water depth gauge 816 using adjustable thresholds 818.

Cistern 814 serves as a storage device for output of well pump motor810.

Adjustable thresholds 818 operate with water depth gauge 816 to providea first, a second, and a third level indication. When water in cistern814 drops below the first threshold, well pump motor 810 is activated bycontroller 804 on power from solar panels 808 if available, and on ACline 812 if not, the pump is activated regardless of AC power costreported by power price receiver 802. This first threshold represents aminimum water level for the cistern requiring filling the cistern at allcosts let water run out.

Should water be above the first threshold and below the secondthreshold, well pump motor 810 is activated by controller 804 on powerfrom solar panels 808 if available, and on AC power only if AC powercost is reported to be low and power from solar panels 808 isunavailable. The second threshold represents a low-reserve level in thecistern, below which the system is authorized to spend on buying cheapAC power.

Should water be above the second threshold but below the thirdthreshold, well pump motor 810 is activated by controller 804 on powerfrom solar panels 808 only if power from solar panels 808 is available;with water above the second but below the third threshold the system isnot authorized to spend on buying power for running the pump motor 810to fill the cistern.

Should water be above the third threshold, all pumping of water ceasesto avoid overflowing the cistern.

The second controller 806 is configured to run a boost pump 820configured to pump water from cistern 814 to pressure tank 822, pressuretank 822 provides water to a building such as a home or business.Pressure tank 822 is fitted with a pressure switch 824 that feeds backto controller 806 to activate boost pump 820 when a water level, andthus pressure, in pressure tank 822 drops below a fourth threshold.

Since boost pump 820 has a higher priority than well pump motor 810,when controller 806 determines from pressure switch 824 that boost pump820 must run, controller 806 communicates with controller 804 todetermine if well pump 810 is operating, if so what power source wellpump 810 is drawing from, and reported power cost.

In high-power-cost periods, controller 806 will run boost pump 820 onsolar power if solar power is available—shutting down well pump 810 ifinsufficient power is available for both pumps 810, 820, but enoughpower is present to run boost pump 820; if no solar power is availablethen controller 806 runs boost pump 820 on the AC line 812. Well pump810 is restarted as soon as the boost pump 820 shuts down

In low-power-cost periods, controller 806 will run boost pump on solarpower if solar power is available and well pump 810 is not running onsolar power, otherwise controller 806 will run boost pump 820 on the ACline 812.

When both pumps 810, 820 are not running, and solar power is available,controller 804 instructs grid tie inverter 826 to divert power back intothe AC line 812.

The system of FIG. 8 thus optimizes electric power charges for powerdrawn from AC line 812 by using storage capacity in the cistern. Thesystem runs the well pump 810 when costs are high only if the cistern isnearly empty (below the first threshold), and runs the well pump 810when costs are low and the cistern is low (below the second threshold)or when solar power is available, coordinating pump operation to avoidoverloading the solar panels 808.

FIG. 9 illustrates components includable in a variable-frequency, MPPT,controller 900 that may be retrofitted to existing capacitor-start ACinduction motor 602 to adapt it to perform as for the system 600illustrated in FIG. 7 . For simplicity, components having the samefunction in FIG. 9 as in FIG. 7 have the same reference number.

At the motor, a connection normally provided between the starting relayor start switch 621 and the starting winding is disconnected, power fromthe starting relay or start switch 621 is coupled to a starting relayconnection SR of controller 900 instead. Controller 900 has a startwinding SW output that is wired to the starting winding 616 of motor 602instead. Controller 900 also has a main winding output Main that iswired to the running winding 612 of the motor 602. The controller has anAC line input 902 and AC neutral input 904 to operate the motor when ACpower is available. A direct-current solar-power input 906 is providedto bring power from a solar array 908, where solar current is monitoredby a metering circuit 910; solar current and voltage are input to themicrocontroller 162 for use by the MPPT firmware.

AC-Start, Solar Run

An alternatives solar hybrid solution for single phase motors withstarting capacitors solves the problem insufficient solar power forstarting a single-phase AC motor but having enough solar power to runthe single-phase motors off of solar differently. Instead of thelow-frequency, low-voltage “soft-start” method discussed above withreference to FIG. 5 , grid power is used to start the motor and motoroperation is switched to solar operation after motor rotation hasstarted.

In an embodiment, a motor control system for induction-type AC electricmotors having starting and running windings has a multiphase VFD drivewith first and second phase outputs. A switching device that connectsthe system to the AC source (electrical grid) can be either ON or OFF.The VFD outputs can be turned OFF to avoid driving the grid.

In the ON setting of the switching device the single-phase motor isconnected to the AC grid, similar to the way the motor would beconnected when powered directly from the AC source. the VFD drive isalso connected to the motor, with its outputs disabled. In a particularembodiment, when the switching device is ON the AC source generates arectified DC link voltage Vdc that powers the VFD device itself, soduring the time the single-phase motor is powered from the AC source theVFD is grid powered, enabling its microcontroller to operate. However,while the switching device is ON the VFD does not perform powerconversion although its microcontroller observes solar intensity todetermine if there is enough solar power to run the single-phase motor,and it can be connected to other devices and receives external signals,like utility signals, and derive decision on when to switch to runningthe single-phase motor off solar power.

In the OFF setting of the switching device, the single-phase motor isconnected to the VFD device output only, and the AC source isdisconnected. Hence the motor is from power generated by solarphotovoltaic panels through the boost circuit at the input of the VFD.

The motor system 240 of FIG. 10 shows a single-phase motor 280 modifiedto have 3 leads where: line wire 261 and neutral wire 262 are supplyingvoltage across the running (or main) winding 282, while start wire 263and neutral wire 262 provide voltage across the starting winding 281.All three leads 261, 262, 263 are connected to the single-phase ACsource 241 and two leads from variable frequency drive 250 throughseparate switch or contactor 242 as shown in the FIG. 10 .

Line 261 and neutral 262 leads are connected to AC line 291 and neutral292 connections of the AC input 241 respectively through contactor 242,or to PH1 254 and PH2 255 connections of the VFD 250. Start winding lead263 is connected to the main winding lead 261 through contactor switch242. In an embodiment, contactor 242 is one or more electronic switchingdevices. In an alternative embodiment, contactor 242 is anelectromechanical relay.

Contactor 242 is operated by microcontroller 252, which in an embodimentis part of the VFD device 250.

If the DC source is solar photovoltaic panels (PV) 253, then themicrocontroller 252 or any other logical device may also have a solarirradiance (sun intensity) sensor 257 and/or a voltmeter and ammetercoupled to the photovoltaic panels and adapted to sense when solarintensity is above a predefined threshold.

There may be an additional external communication port 258 adapted toreceive commands from other devices or systems including a motoroperation desired signal and couple these to the microcontroller 252. Insome embodiments, the microcontroller receives a utility signal, whichcan request use of solar energy for running the single-phase motorduring high peak power hours, or signals from a demand/responsesubsystem coupled to or operated by the motor. For example, themicrocontroller may receive a high-cost electricity warning signal fromutility, and if it decides that there is enough solar power available,the microcontroller switches supplied power for the single-phase motorfrom AC source to the solar source. In another example, themicrocontroller receives “temperature dangerously high” (indicatingmotor operation is critical) and “cooling desired but not essential”(indicating motor operation is desired but not critical) signals from anHVAC air conditioning or refrigeration system; the microcontroller beingconfigured to start the motor on AC power if either enough solar poweris available to run the motor and motor operation is desired but notcritical, to start the motor on AC power if motor operation is critical,and to then switch to running the motor on solar power if enough solarpower is available.

Boost circuit 251 is a DC-to-DC converter that connects the solar PVsource 253 with a VFD device incorporating four high speed powerswitches: Q11-Q14 driven by the PWM signals 256 from microcontroller252. In a particular embodiment, boost circuit 251 is an up-converterwith a higher output voltage than input voltage.

Microcontroller 252 obtains the solar current information throughcurrent sensor 271 and voltage information, as well as DC link voltageinformation. Once powered, microcontroller 252 decides if there isenough solar power to switch motor operation to solar power only, inwhich case it turns contactor 242 OFF, and the VFD device takes overrunning the motor with solar power supplied from the Solar PV source,using solar power conditioned by boost circuit performing the MPPTmethod 990 described with reference to FIG. 5 to extract maximum poweravailable from the solar PV panels. In this MPPT method 990, when solarpower received from the solar panels is insufficient to maintain the DClink voltage at a regulated level determined by the microcontroller, themicrocontroller steps down the DC link voltage (and thus the AC voltageprovided by the VFD to the motor) and VFD operating frequency by stepsof a first size. When solar power received from the solar panels isample to maintain the DC link voltage at the regulated voltage, themicrocontroller may step up the DC link voltage (and thus AC voltageprovided by the VFD to the motor) and VFD operating frequency in stepsof a second size, steps of the second size being smaller than steps ofthe first size. The microcontroller remembers the last voltage andfrequency tried before the step where it was necessary to step downfrequency and voltage and may reset the DC link voltage and VFDoperating frequency to that last voltage and frequency for a time beforeonce again increasing DC link voltage and VFD operating frequency.

Operation of the embodiment of FIG. 10 is according the method 950 ofFIG. 11 , beginning 952 when motor operation is desired. Microcontroller252 checks 954 the insolation sensor to see if sufficient power isavailable to run the motor. If sufficient solar power is available torun the motor, the contactor is set 956 to AC power and the motor isstarted 958; as soon as the motor is started, microcontroller 252optionally phase-synchronizes 960 the VFD to the AC power, turnscontactor 242 off 964, and enables the VFD to power the motor with solarpower without stopping the motor.

Phase-synchronization of VFD to AC power may be understood withreference to FIG. 12 depicting voltage 1001 across the run winding 282of motor 280. During time 1002 the AC motor is starting on AC power,voltage 1001 across the run winding matches that of AC line power. Whenthe motor has started, as determined by a timeout or by sensing currentat motor 280, contactor 242 is opened at time 1008. In a particularembodiment contactor 242 is an electronic switching device and is openedat a zero crossing of current applied to motor 280. Once contactor 242is opened, the VFD provides an AC voltage, here a pseudosine waveform,during a time 1004, 1006 that the motor runs on solar power provided bythe VFD; the first cycle of AC power provided by the VFD includes apulse 1010 of the same polarity or phase and approximately the samevoltage as would have been provided 1012 by the now-disconnected ACpower and centered at a time where the next half-cycle of thenow-disconnected AC power waveform would have peaked. The VFD does not,however, need to maintain the same operating frequency as the AC powerif available solar power is less than that required to run the motor atfull speed, in later half cycles during time 1006 the motor may beprovided with AC power with voltage and frequency reduced better matchpower consumed by the motor to available solar power at the maximumpower point.

Once the VFD is powering the motor, motor speed and voltage are adjusted966 as necessary to maintain voltage at the solar panels at the maximumpower point if available solar power is less than needed for full speedoperation, or at full speed if sufficient solar power is available,using an MPPT method 990. Motor operation continues until operation ofthe motor is no longer desired or the motor cannot maintain a minimumspeed because solar power available has dropped, at which point the VFDis disabled to stop 970 the motor. If the motor was stopped because themotor could not maintain minimum speed on the available solar power, thesystem waits a predetermined cooling-off time before trying again.

Should insufficient solar power be available to run the motor,microcontroller 252 checks 972 to see if motor operation has becomecritical, such as when water levels in a reservoir drop below a minimumlevel or temperatures in a freezer rise to melting. If motor operationis not critical, the system waits. If motor operation is critical,contactor 242 is turned on 976, starting 976 the motor on AC power.Since insufficient power is available, contactor 242 remains on and themotor runs 978 on AC power while the microcontroller 252 periodicallychecks 980 if sufficient solar power is available to run the motor. Ifsufficient solar power is now available to run the motor, operation ofthe motor is switched to solar power by optionally phase-synchronizes960 the VFD to the AC power, turning contactor 242 off 964, and enablingthe VFD to power the motor with solar power. If sufficient solar poweris not available to run the motor, microcontroller 252 checks 982 to seeif motor operation is critical and desired, and if so continues running978 the motor on AC power. Once motor operation is not desired or nolonger critical, contactor 242 is opened 984 to stop the motor.

In an alternative embodiment without a solar insolation sensor, themicrocontroller assumes at a first pass of 954 that sufficient AC poweris available to run the motor, starts 958 the motor on AC power, andtries running 964 the motor on solar power. If the motor then stops 970for want of solar power, the microcontroller checks 972 if motoroperation is now critical and restarts the motor and runs it as neededon AC power.

AC Start, Solar Run, with Solar Power Availability Testing

Single phase motor loads can be controlled such that their frequency ischanged in a range 50-100% of nominal frequency (50 Hz or 60 Hz) tomatch motor power to available power. Depending on the motor and what itis driving, the motor power can be linear, square or cube in respect tothe AC motor frequency. Power is linearly proportional to the frequencyfor compressor loads, while cubic relationship of consumed power tofrequency is more common for pump and fan motor loads. Thus, power torun the motor load at 50% of its nominal frequency (the power levelwe've defined as the minimum running power) can be significantly lessthan half of its nominal power consumption (at 100% of the frequency).

We propose embodiments with four ways of measuring available solar PVpower to determine if the system should be started, then, if power isadequate, start the motor on AC grid power before reverting to operationon the available solar power:

One embodiment, illustrated in FIG. 13 with associated text below, usesa power switch at the output of solar panels or input of a solar motorcontroller to create a short circuit condition over the solar PV panels,such that a microcontroller can measure short circuit current I_(SC).This I_(SC) current is directly proportional to solar irradiance acrossa panel, hence provides information on solar PV power availability. Whenthis switch is open, the microcontroller measures the open circuitvoltage V_(OC) of the solar PV system. Based on short circuit currentI_(SC) and open circuit voltage V_(OC), the microcontroller can estimateavailable power SPA of the solar PV panels, and compares SPA to thepre-measured minimum running power for a motor. This way it's possibleto decide when to start the motor from the grid with intent to switch tosolar only operation with using solar PV power to run the motor load ator above minimum operational frequency.

Another embodiment, illustrated in FIG. 14 and described below, uses apower switch 1402 in series with a power resistor 1404, connected to theDC positive and negative sides of the DC link circuit. Thus, if thispower switch 1402 is ON, the resistor 1404 is directly powered by DClink voltage, across the DC+ and DC− nodes, and if this power switch isOFF, then the resistor is removed from the DC link circuit. In this casepower resistor serves as the only load for the solar PV panels 253because the VFD is temporarily shut off during the measurement. With thepower resistor in the circuit, using current sensor 271 and ananalog-digital converter input of the microprocessor, we measure solarPV current and voltage respectively, where boost circuit 251 finds agood MDPT operating point over the power resistor 1404. Thus,microcontroller 252 can calculate available solar PV power SPA anddetermine whether SPA is sufficient to run the motor.

This embodiment need only measure power briefly after which the motormay be started or the resistor is disconnected, allowing use ofresistors with heat dissipation ratings significantly below maximumavailable solar power.

A similar embodiment is shown on FIG. 15 , where power resistor 1404 isplaced between DC− node of the DC link and output of third phase of athree phase variable frequency drive (VFD). Thus, an off-the shelf VFDoutput section can be used in this configuration. The VFD acts as powerswitch 1402 to apply power to the resistor while power is beingmeasured.

A fourth embodiment with hardware as illustrated in FIG. 10 uses theVariable Frequency Drive (VFD) circuit in a buck mode feeding motorphase resistance as a load to the solar PV input circuit withoutactually starting the motor—motor rotation is inhibited by not drivingthe start winding. In this embodiment, the solar PV panels are brieflyloaded with the motor run-phase winding resistance; to avoid undueheating of the motor, power is only applied to the run-phase windingbriefly. Thus, it's possible to measure current and voltage receivedfrom the PV panels, and microcontroller 252 can calculate solar PV powerSPA a by multiplying current time voltage and determine whetheravailable power SPA from the solar PV panels is sufficient to run themotor.

Once available power has been measured and determined above a firstmotor-and-load dependent threshold, the system may proceed to apply ACpower to the motor's run-phase winding, phase-shifted AC power to themotor's starting winding, and attempts motor starting. If availablesolar power is above the first threshold, and below a second threshold,the system uses AC power to start the motor, then reverts to poweringthe motor exclusively from solar power once the motor is started. Ifmotor starting fails or available power is below the first threshold,the system waits for a time and repeats the process of measuringavailable solar power and attempting startup if the available solarpower is sufficient to run the motor.

In some embodiments, the first threshold is a dynamic thresholddetermined from prior operations of the motor by observing periods ofsuccessful motor operation and events where the motor was started butsolar power proved insufficient to run the motor; this dynamic thresholdis stored in microcontroller memory for future use.

The motor system 1300 of FIG. 13 shows a single-phase motor 280 modifiedto have 3 leads where: line wire 261 and neutral wire 262 are supplyingvoltage across the running (main) winding 282, while start wire 263 andneutral wire 262 provide voltage across the starting winding 281. Thosethree leads are connected to the single-phase AC source 241 and twoleads from variable frequency drive 250 through separate switch orcontactor 242 as shown in FIG. 10 .

Line 261 and neutral 262 leads are connected to AC line and neutralconnections of the AC input 241 respectively through contactor 242, orto PH1 254 and PH2 255 connections of the VFD 250. Start winding lead263 is connected to the main winding lead 261 through contactor switch242.

Contactor switch 242 can be energized (actuated) by signal that can bederived from the microcontroller 252, which is part of the VFD device250, or some other device with simple signal logic outputs, or manuallyusing a switch.

In this embodiment, if the DC source is Solar photovoltaic panels (PV)253, then the microcontroller 252 measures available solar PV power byusing power switch 1302, which is positioned to short across solar PVpanel outputs 253 through current circuit measurement device 1304. Oncethe switch 1302 is closed by microcontroller signal, and short circuitsthe solar PV panel(s) then short circuit current I_(SC) of the solar PVpanels is measured by current sensor 1304 and provided to themicrocontroller. Once the power switch 1302 opens then microcontrollerreads the open circuit voltage V_(OC) from the solar PV panels. Themicrocomputer then multiplies V_(OC) by I_(SC) and compares the productSPA to the first and second thresholds. Thus, it is possible to estimatesolar PV power in a real time using current and voltage sensors andpower switch, to determine if the available solar PV power would besufficient to run the single-phase motor load, and thus engage gridpower using contactor 242, after which the motor load would start andmotor load would be driven by solar PV 253 only using variable frequencydrive power switches. There is no need for external solar irradiancesensors.

FIG. 14 shows another embodiment 1400, with power switch 1402 in serieswith a power resistor 1404 as shown. When power switch 1402 is closed bythe microcontroller 252, then power resistor 1404 is connected acrossthe DC link rails DC+ and DC−. In this case, power resistor 1404 servesto load for the solar PV panels 253. Current sensor 271 and voltagesensor 272 are used by microcontroller to measure solar PV current andvoltage respectively, where boost circuit 251 is used for performingMPPT operation over the power resistor 1404 in a brief time. Thus,microcontroller 252 can calculate available solar PV power SPA.

If the power switch 1402 is OFF then the power resistor 1404 is not inthe DC link circuit at all.

FIG. 15 shows another embodiment 1500, with power resistor 1502connected to the third phase of a three phase VFD incorporatingtransistors 1506 and 1508, and a DC− rail of the DC link, as shown. Inthis embodiment, the first two phases 254, 255, of the VFD couple to run282 and start 281 windings of the motor, respectively, and the thirdphase 1504 is configured to selectively apply power to resistor 1502 orbypass resistor 1504.

In a fourth embodiment, solar PV power is measured in real-time, withoutadded power switches or resistors. If boost circuit 251 is optionallybypassed, then solar PV 253 output are directly connected to the DC linkrails DC+ and DC−. When contactor 242 is turned OFF, and there is no ACgrid input 241, then power switches of the variable frequency drive ascontrolled by microcontroller 252 signals 256 can apply power to phaseconnections 254 and 255 of single phase motor 280, such that runningwinding 282 is positioned across the variable frequency drive output(VFD) phases 254 and 255. Hence, microcontroller 252 can control powerswitches of the VFD to provide voltage across phases 254 and 255 andthereby use running winding 282 as a load to the solar PV input source253. Again, current and voltage sensors 271 and 272 respectively areused to measure solar PV 253 available power SPA.

In all four embodiments, once SPA is determined or estimated, SPA iscompared to a first threshold VT₁ and to a second threshold VT₂. If SPAis greater than both VT₁ and VT₂, the system starts the motor usingsolar power. If SPA is greater than VT₁ but less than VT₂, the systemstarts the motor using power from an external AC source. Once the motoris running, the system continues to run the motor on solar power untilmotor operation is no longer necessary.

Changes may be made in the above methods and systems without departingfrom the scope hereof. It should thus be noted that the matter containedin the above description or shown in the accompanying drawings should beinterpreted as illustrative and not in a limiting sense. The followingclaims are intended to cover all generic and specific features describedherein, as well as all statements of the scope of the present method andsystem, which, as a matter of language, might be said to falltherebetween.

What is claimed is:
 1. A system comprising: an AC electric motor of thesingle-phase induction type; the AC electric motor having a startwinding, and a run winding; an AC input connection; a variable frequencymotor (VFD) drive having at least a first and a second phase output, theVFD drive coupled to be powered by a solar panel input; a contactorhaving at least a first and a second setting; wherein, with thecontactor in the first setting, at least one output of the VFD isconnected across the run winding of the AC electric motor; and with thecontactor in the second setting, the run winding of the AC electricmotor is coupled to the AC input connection and the start winding of theAC electric motor is coupled through a capacitor and start switch to theAC input connection; wherein the system is configured to, upondetermining that the motor has started rotating, setting the contactorin the first setting, the variable frequency motor drive thereupon beingconfigured to continue running the motor by applying AC voltage acrossrunning winding only, the VFD drive configured to use power from thesolar panel input; and when the AC electric motor is not rotating, andmotor operation is desired, the system is configured to periodicallymeasure an available solar power and to start the AC electric motor ifthe available solar power is greater than a first threshold powerdetermined to be sufficient to run the AC electric motor.
 2. The systemof claim 1 wherein the system is configured to measure available solarpower by measuring an open-circuit voltage V_(OC) at the solar panelinput and a short circuit current I_(SC) at the solar panel input. 3.The system of claim 2 wherein the system is configured to compare theavailable solar power to a second threshold and, if available solarpower is greater than the second threshold, to start the AC electricmotor by applying from the VFD drive a first phase AC power to the runwinding of the AC electric motor and a second phase AC power to thestart winding of the AC electric motor; and, if available solar power isgreater than the first threshold and less than the second threshold, tostart the AC electric motor by applying power from the AC inputconnection.
 4. The system of claim 3 wherein the first and secondthresholds are determined from success or failure of prior attempts tostart the AC electric motor.
 5. The system of claim 1 wherein the solarpanel input is coupled to the VFD drive through a DC to DC voltageconverter, and where the system is configured to measure the availablesolar power by coupling a resistor across an output of the DC to DCvoltage converter and measuring voltage at the solar panel input and acurrent at the solar panel input.
 6. The system of claim 5 wherein thesystem is configured to compare the available solar power to a secondthreshold and, if available solar power is greater than the secondthreshold, to start the AC electric motor by applying from the VFD drivea first phase AC power to the run winding of the AC electric motor and asecond phase AC power to the start winding of the AC electric motor;and, if available solar power is greater than the first threshold andless than the second threshold, to start the AC electric motor byapplying power from the AC input connection.
 7. The system of claim 5wherein the first and second thresholds are determined from success orfailure of prior attempts to start the AC electric motor.
 8. Theapparatus of claim 1 wherein the system is configured to measure theavailable solar power by placing the contactor is in the second setting,and applying power from the solar panel input through the VFD drive tothe run winding of the induction-type AC electric motor while the ACelectric motor is not rotating.
 9. The system of claim 8 wherein thesystem is configured to compare the available solar power to a secondthreshold and, if available solar power is greater than the secondthreshold, to start the AC electric motor by applying from the VFD drivea first phase AC power to the run winding of the AC electric motor and asecond phase AC power to the start winding of the AC electric motor;and, if available solar power is greater than the first threshold andless than the second threshold, to start the AC electric motor byapplying power from the AC input connection.
 10. The system of claim 9wherein the first and second thresholds are determined from success orfailure of prior attempts to start the AC electric motor.
 11. The systemof claim 2, the system configured to perform maximum power pointtracking.
 12. The system of claim 5, the system configured to performmaximum power point tracking.
 13. The system of claim 8, the systemconfigured to perform maximum power point tracking.
 14. A method ofstarting and running an AC induction motor using solar power from asolar power input comprising: measuring available solar power at thesolar power input; determining whether the available solar power exceedsa first threshold but does not exceed a second threshold, and if theavailable solar power exceed the first threshold but does not exceed thesecond threshold, starting the AC induction motor with power from an ACinput, and, once the AC induction motor has started switching to run theAC induction motor with a variable frequency motor drive powered by thesolar power input; determining whether the available solar power exceedsthe first threshold and exceeds the second threshold, and if theavailable solar power exceeds the first threshold and exceeds the secondthreshold, starting the AC induction motor with power from the variablefrequency motor drive powered by the solar power input.
 15. The methodof claim 14 wherein the available solar power is determined by shortingacross the solar power input and measuring a short circuit current andmeasuring an open circuit solar power input voltage.
 16. The method ofclaim 14 wherein the available solar power is determined by placing aresistive load on a DC-DC converter driven by the solar power input andmeasuring a voltage at the solar power input.
 17. The method of claim 14wherein the available solar power is determined by applying a voltagethrough the variable frequency motor drive to a winding of the ACinduction motor and measuring a voltage at the solar power input.